Patent GB-814943-A (GB)
Title: Improvements in or relating to automatic telephone exchanges
Inventor: HOPLEY HORACE EDWARD
IPC: H04Q3/00
Filed: 1955-01-26
Abstract: 814,943. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Dec. 9, 1955 [Jan. 26, 1955], No. 2320/55. Addition to 718,056. Class 40 (4). In a telephone exchange in which subscribers' lines are multipled to corresponding crosspoints in a plurality of bridges of a cross-bar switch, a plurality of link circuits for completing connections are provided, each link circuit being connected to a pair of bridges of the switch, and one or more control circuits are directly accessible from the link circuits. Non-numerical switching.In the normal state relay DR in the alloterALL is operated, as also is one of relays RA, RB (say RA) which respectively pre-allot one control circuit 1CC, 2CC for use in the next call and also one of relays LA ... LD (say LA) which pre-allots one of four transmission relay sets or feedbridges such as 1TRS. Assume say line 31 is calling, then operation of its line relay LS brings up GB (indicative of the tens group to which it belongs) in series with select magnet ISM. Relay GB disables GA (corresponding to the other tens group) and short circuits its own high resistance winding to operate the select magnet ISM. This operates DA in the allotter, and DL follows to bring up the group switching relay WSA in the allotted transmission relay set 1TRS (since GB is up). Relay DL also operates SA to connect the transmission relay set to the allotted control circuit 1CC. DL also brings up RB to pre-allot control circuit 2CC if the latter is free. In the transmission relay set SA now brings up E and the originating bridge magnet 1BM to complete the connection from the subscriber's line circuit SLC to the transmission relay set. Cut-off relay K in SLC is thereby operated to complete the switch-through, whereupon LS releases and impulse relay A in the transmission relay set operates followed by B which brings up BB, TA and PA in the control circuit. Meanwhile the slow release of DR consequent upon the operation of DL effects release of 1SM, GA, LA, RA, DA, the last releasing DL to re-operate DR. When DL operated it brought up LB which remains up to pre-allot the next transmission relay set 2TRS (not shown). In the control circuit PA connects up dial tone and operates CD by removing a shunt, and CE follows. Receipt of digits and completion of connection.- The dial break impulses are repeated by A as make impulses to AA in the control circuit. On the first make of contact aa1 PB operates in series with PA via contact pa2 and when aa1 subsequently releases PA releases since its holding circuit over resistance R12 has now been transferred by contact pb2 to relay PB. Each successive impulse steps the chain PA ... PL similarly. Assuming the wanted subscriber is number 20, then at the end of the first digit PC remains operated. At the end of the digit CD is released by short circuiting and CE follows, whereupon relay FD operates over the strapping 2-FD in the terminal field FDF. If digit 3 is dialled relay WS is brought up over strapping 3-WS and FD follows. Relay WS brings up group switching relay WSB in the transmission relay set. Relay FD releases PC to restore the counting chain. When CE releases PA re-operates followed by CD, CE. The second digit (O) is now registered, PL remaining operated at the end of the train, the release of PA releasing SD. Relays CD, CE release as before and bring up DT in the allotter which prevents intrusion by an incoming call. Relay SZ now comes up in control circuit 1CC thereby disabling control circuit 2CC, and DS follows to disconnect the allotter chains LA ... LD and RA, RB. Relay DS also brings up select magnet 10SM indicated by PL. Relays DA, DL follow in the allotter to release DR and bring up the terminating bridge magnet 5BM to connect 1TRS through to the wanted subscriber's line circuit and to bring up TC. The latter releases the control circuit and the allotter. If the called line is idle, H comes up in series with the called subscriber's K relay during the operating period of TC. Relay E then releases to connect up ringing current and on reply the ring-trip relay F operates to connect up the back-bridge relay. Conversation then proceeds on a calling party release basis. If the called party is busy H fails to operate and when E releases busy tone is reverted. The transmission relay set contains a balancing network R6, C3 switched in when A or D is back to prevent howling of a subscriber's loudspeaking telephone when the other subscriber is on-hook. Privileged intrusion on busy line.-Privileged subscribers have their D terminals connected to the P-wire. A call is set up in the normal manner, but if H fails to operate, then when TC releases, the earth on the calling subscriber's P-wire is extended over the D-terminal to bring up relay D and F follows. The caller may now intrude on the existing conversation. When the parties thereto hang up on request, H operates in series with the wanted subscriber's K relay and releases D, F and E. Ringing now takes place and the call proceeds as in the normal case. Calls to special lines (first digit O).-When O is dialled counting relay PL brings up relay OL and FD follows. The second digit (7, 8, 9 or 0) then operates either PH, PJ, PK or PL to effect operation of select magnet 11SM or 12SM and, if necessary, relay WS over strappings of the terminal field SDF. Completion of the connection then takes place in the normal way. Codes 01 ... 06 are spare (see below). Inter - exchange tie - lines.-Ordinary subscribers' line circuits are used for these, but in addition to the PN terminals being connected to the P-wire the DN terminals are earthed, so that when a call is established to such a line circuit relay TL is operated. This operates F and loops D across the line. D operates to battery from the distant exchange and when dial tone is received therefrom the further dialled digits are repeated thereto by contact a1. Relay E operates during impulsing to provide a clean outgoing impulsing loop. Tie-line group (of 2 lines).-Two lines forming such a group are given the same units digit, connection to the second when the first is busy being effected by operating the switching relay WSB. In addition to the above-mentioned connections of DN and PN, the P-wire of the first tie-line is strapped to the relevant terminal in the field TLGF. E.g., if the tie-line numbers are 20 and 30, terminal O is strapped to the P-wire of subscriber number 20. When the number 20 is dialled, if the line is busy then during the slow release of CE, relay WS operates over this strapping to the busy earth on the P-wire and so brings up WSB. Connection then takes place to line circuit number 30, and busy tone is reverted or switch-through effected in accordance with the state of the line. Spare codes.-If 1 or 4 ... 9 is dialled as a first digit then when CD releases earth extended over terminal SC (FDF) holds CE and operates bridge magnet SBM and TC follows. Since no select magnet has been operated, no connection is made to the transmission relay set and H cannot operate so that busy tone is returned. If two lines sharing the same units digit are both spare, the corresponding terminal is connected to SSC in field SDSF. If only one of the lines is spare its terminal is connected to WSN or WSO according to the tens group to which it belongs. Earth over this field is then used to hold CE and operate 5BM with the same result as above. If any of lines 07 ... 00 are spare the corresponding terminals in field SDF are strapped to terminal SC (FDF) with a similar result. With 01 ... 06 as permanent spares contacts pb1 ... pg1 are permanently connected to terminal SC. Tuned release.-When relay TA operates on seizure of the control circuit, thermal relay TH is energized. When the latter eventually operates it brings up TB and disconnects itself. When it releases again magnet 5BM is operated and busy tone is returned as in the case of spare codes. 2-Party lines.-Each party has a separate number and the corresponding positions in the cross-bar switch are connected to the + and - wires of Fig. 6, the speech wires being reversed in one case. This permits the respective parties to be rung over different legs and earth. The party line is connected to terminals A, B. The PN terminal, Fig. 6, is connected to the corresponding two terminals in the field PN, Fig. 5. The line relay set SLC of one of the parties is disconnected and the D-terminal corresponding to the line relay set that is retained is connected to the corresponding D-terminals, Fig. 3. Normal calls are effected in the usual way. When a revertive call is to be made a calling subscriber takes a transmission relay set and a control circuit into use in the usual way and dials a special digit. The corresponding terminal in the field FDF is strapped to terminal RC and earth is extended thereover to terminal D to bring up 1RA, Fig. 6. Relay 1RB follows, puts guarding earth on terminal PN, loops IRA across the party line and opens the D.C. path to the transmission relay set. Condensers C4 and C5 ensure that a priveleged subscriber may still intrude upon the call. The caller then hangs up releasing 1RA, thereby bringing up RCR which connects earthed ringing current from lead IR to the A-wire and battery and ringing current from transformer TR 1 to the B-wire. When the called party answers RF responds releasing RCR to reconnect 1RA to the loop, the latter re-operating and supplying talking battery for both parties. Fire alarm and night watchman's circuit, Fig. 7.-Each portion of Fig. 7 replaces a subscriber's line circuit. A wire M, a lamp FAL and a magnet WCM are provided for each substation from which a watchman's or a firealarm call may be made. A watchman dials a special two digit number and obtains access to the circuit WMS in the usual way. Relay H operates in series with KA over the PN wire and the retard IA trips the ringing. Relay D does not operate due to battery on the righthand win